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| Titel |
The trophic and metabolic pathways of foraminifera in the Arabian Sea: evidence from cellular stable isotopes |
| VerfasserIn |
R. M. Jeffreys, E. H. Fisher, A. J. Gooday, K. E. Larkin, D. S. M. Billett, G. A. Wolff |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 6 ; Nr. 12, no. 6 (2015-03-18), S.1781-1797 |
| Datensatznummer |
250117868
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| Publikation (Nr.) |
 copernicus.org/bg-12-1781-2015.pdf |
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| Zusammenfassung |
| The Arabian Sea is a region of elevated productivity with the highest
globally recorded fluxes of particulate organic matter (POM) to the deep
ocean, providing an abundant food source for fauna at the seafloor. However,
benthic communities are also strongly influenced by an intense oxygen
minimum zone (OMZ), which impinges on the continental slope from 100 to
1000 m water depth. We compared the trophic ecology of foraminifera on the Oman
and Pakistan margins of the Arabian Sea (140–3185 m water depth). These
two margins are contrasting both in terms of the abundance of sedimentary
organic matter and the intensity of the OMZ. Organic carbon concentrations
of surficial sediments were higher on the Oman margin (3.32 ± 1.4%) compared to the Pakistan margin (2.45 ± 1.1%) and
sedimentary organic matter (SOM) quality estimated from the Hydrogen Index
was also higher on the Oman margin (300–400 mg HC mg TOC−1) compared to the
Pakistan margin (< 250 mg HC mg TOC−1). The δ13C and δ15N
values of sediments were similar on both margins (−20 and 8‰, respectively). Stable
isotope analysis (SIA) showed that foraminiferal cells had a wide range of
δ13C values (−25.5 to −11.5‰), implying that they utilise multiple food sources;
indeed δ13C values varied between depths, foraminiferal types
and between the two margins. Foraminifera had broad ranges in δ15N values
(−7.8 to 27.3‰). The enriched values suggest that some species may store nitrate to
utilise in respiration; this was most notable on the Pakistan margin.
Depleted foraminiferal δ15N values, particularly at the Oman
margin, may reflect feeding on chemosynthetic bacteria. We suggest that
differences in productivity regimes may be responsible for the differences
observed in foraminiferal isotopic composition. In addition, at the time of
sampling, whole jellyfish carcasses (Crambionella orsini) and a carpet of jelly detritus were
observed across the Oman margin transect. Associated chemosynthetic bacteria
may have provided an organic-rich food source for foraminifera at these
sites. Our data suggest that foraminifera in OMZ settings can utilise a
variety of food sources and metabolic pathways to meet their energetic
demands. |
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